In a Denial of Service (DOS) attack, a human adversary employs one or more client computers connected to the Internet, and compromises them by installing a DOS software on them. The human adversary then commands the compromised computers, using the installed DOS software, to send large volume of traffic having bogus requests to an Internet-connected server requesting services from it. It is possible that the server could not be able to differentiate between a legitimate request and a bogus request, since a bogus request can have the correct format as a legitimate request. Thus, the victim server gets overwhelmed by the large amount of requests and cannot even provide services to legitimate requests. DOS attacks are primarily launched against high-profile web sites/servers such as Yahoo®, E-Trade®, Amazon®, CNN®, and so on.
Therefore, there is a need for a countermeasure solution for protecting servers against DOS attacks that enables victim servers to sustain service availability during such attacks in such a manner that addresses at least some of the problems associated with conventional countermeasures.